Conventional intake air devices generate a gas flow such as swirling or tumbling of the intake air introduced into a combustion chamber of an internal combustion engine by providing an intake airflow control valve in the intake air path and controlling the opening and closing of the valve.
As disclosed in Laid Open Japanese Patent No. 2003-239749, a conventional intake air device introduces into a combustion chamber an intake airflow deviated in the upper side of the intake air path by using an intake airflow control valve having an opening with an opening area on the top. In this device, turbulent airflow can be generated in the combustion chamber by the intake airflow that passes through the main opening.